It is known in the prior art that the formation of groups of large crystals in molten metal may be inhibited by subjecting the molten metal to high frequency vibrations. In recognition of this fact, prior attempts have been made to subject molten metal to such vibrations immediately prior to casting. For example, early suggestions included applying high frequency vibrations to crucibles containing molten metal to be cast. For the most part, however, attempts to vibrate crucibles have proved unsuccessful. Most crucibles are formed of ceramic material and do not conduct vibrations very well. Furthermore, a crucible is a relatively massive structure and vibrating such a structure generates significant power losses.
A further suggestion for subjecting molten metal to high frequency vibrations immediately prior to casting is found in U.S. Pat. No. 2,419,373 to Schrumn, wherein a solenoid cone is precisely fitted in the bottom of a cylindrically shaped static mold for applying ultrasonic vibrations. Longitudinal vibratory movements are applied to a core, which vibrations are, in turn, transmitted to molten metal poured into the mold. The molten metal is allowed to cool and solidify while vibrations are applied by the solenoid cone.
The application of ultrasonic vibrations to static casting molds is also disclosed in U.S. Pat. No. 2,897,557 to Ornitz and U.S. Pat. No. 3,678,998 to Tien et al. In Ornitz, a fusible metal member is inserted into a casting mold and subjected to vibrations. The inserted metal member has a composition that is either the same as or compatible with the cast product and is substantially melted and dispersed into the cast product during the solidification process.
In the aforementioned Tien et al patent, a probe is inserted into the upper end of a static mold for a molten metal casting. The probe applies ultrasonic vibrations to the molten metal during the solidification process. In order to prevent capture of the probe by the solidified metal, the probe is positioned away from a chill plate for cooling the metal and is removed from the metal before the solidification front reaches a point to encompass the probe.
A method and apparatus for casting metal dental castings, jewelry and other precision castings is disclosed in U.S. Pat. No. 3,461,942 to Hoffman et al. A mold has a cover with an opening for the insertion of a vibrating probe connected to a transducer. The Hoffman et al reference teaches casting of different metals upon each other in layers while simultaneously subjecting the metals to heating and vibratory movement from the probe. The different metals are cohesively bonded in layers without substantial intermixing.
In U.S. Pat. No. 2,820,263, a special ladle having an ultrasonic generator or transducer in its handle is disclosed. The vibrations applied to the ladle are transmitted to molten metal as it is being transported between a crucible and a mold.
The application of ultrasonic vibrations to a continuous casting is taught in U.S. Pat. No. 3,512,401 to Thalmann. A cooling body is positioned closely above a relatively moving hot metal casting. A cooling agent, preferably water, is introduced into the cooling body for flowing contact with the hot casting. An ultrasonic transducer applies a vibratory movement to the flowing water which, in turn, couples the vibrations to the hot casting.